The impact of positive end-expiratory pressure on functional residual capacity and ventilation homogeneity impairment in anesthetized children exposed to high levels of inspired oxygen

BACKGROUND: High fractions of inspired oxygen (FIO2) result in resorption atelectasis shortly after their application. However, the impact of different levels of FIO2 and their interaction with positive end-expiratory pressure (PEEP) on functional residual capacity (FRC) and ventilation distribution is unknown in anesthetized children. We hypothesized that the use of a FIO2 of 1.0 results in a decrease of FRC and ventilation homogeneity compared with that of a FIO2 of 0.3, and that this decrease is prevented by PEEP of 6-cm H2O compared to a PEEP of 3-cm H2O. METHODS: Forty-six children (3-6 yr) without cardiopulmonary disease were randomly allocated to receive PEEP of 6-cm H2O (PEEP 6 group) during the entire study period or PEEP of 3-cm H2O (PEEP 3 group). The order of the FIO2 (0.3 or 1.0) was also randomized. A defined recruitment maneuver was performed after tracheal intubation and 5 min later the first measurement. This procedure was then repeated with the second FIO2 level. FRC and lung clearance index (LCT) were calculated by a blinded observer. RESULTS: While FRC (mean +/- SD) was similar at both levels of FIO2 (0.3: 25.6 +/- 2.9 mL/kg vs 1.0: 25.6 +/- 2.8 mL/kg, P = 0.189) in the PEEP 6 group, FRC decreased in the PEEP 3 group (0.3: 24.9 +/- 3.8 vs 1.0: 21.7 +/- 4.1, P < 0.0001). Furthermore, with continuous PEEP of 6-cm H2O a similar LCI was observed at both levels of FIO2 (0.3: 6.45 +/- 0.4 vs 6.43 +/- 0.4, P = 0.668) while LCI increased at the higher FIO2 in the PEEP 3 group (0.3: 6.5 +/- 0.5 vs 1.0: 7.7 +/- 1.2, P < 0.0001). CONCLUSIONS: During the application of a very low PEEP of 3-cm H2O, FRC and. ventilation distribution decreased significantly at an FIO2 of 1.0 compared with that at an FIO2 of 0.3. This decrease could be counterbalanced by the administration of PEEP of 6-cm H2O, indicating that a low level of PEEP is sufficient to maintain FRC and ventilation distribution regardless of the oxygen concentration.